restorer-john
Grand Contributor
we do know that discrete amplifiers are not intrinsically more reliable than chip-based amps.
We know do we? I didn't get that memo.
Amplifiers deliver high voltages and high currents on a constant basis into very low impedances. That's what they are supposed to be designed to do. Well designed amplifiers can do that, but IC (chip-amps) based amplifiers need a whole lot of housekeeping to keep them from not blowing up when the going gets tough. They are always a compromise, because their entire existence is driven by minimizing costs.
Discrete amplifiers can parallel up output devices, beef up the power supplies and improve the heat sink efficacy. They can be scaled easily, a basic design can serve multiple price points and performance demands, all while being extremely reliable and low cost, especially when it comes to repair.
A chip-based amplifier (we are talking here OPTs on the substrate, not a 'driver' chip for conventional OPTs) is a take-it or leave-it design, mostly.
Take the biggest and most widely used "chip" based HiFi amplifier devices I can think of. Historic, for perspective in this discussion. Sanyo's thick film hybrids (STKs) from the 1970s through the 1990s. They had many hundreds of STK SKUs. Ranging from single darlington output packs to an entire 150W+ stereo amplifier in a SIL package. Millions and millions sold to OEMs over 3 decades. Pretty much every brand used them at some point. Be it class A driver stages for a real output stage or basically an entire power amp in plastic package.
STK based amplification was sold on cost, ease of assembly and guaranteed performance (it was average at best). Not SOTA, but good enough for Joe Average. They also are renowned for blowing up in the face of difficult loads. You cannot short an STK and expect it to survive. They overheat easily and fail, especially when installed on heatsinks that are too small. They can oscillate and destroy themselves. They sound fine when they are working, but Sanyo discontinued the entire STK thick film range in December 1995 and left everyone out in the cold. Now there are only fakes and very old NOS or Chinese SMD copies that don't work. People have resorted to building discrete equivalents to keep their gear alive. Same thing happened in the 70s/80s when Sanken killed their "amp on a chip" hybrids. People had to reverse engineer the IC or throw their amplifier on the trash. We know most went to landfill...
Here's a nice little complimentary pair of Toshiba outputs I scavenged from a 1980s amplifier I found on the side of the road. About AU$7 per piece to buy today. Yes, you can still buy them!
High voltage : check! 180V Vce
High current : check! 12A Ic max
High dissipation : check! 130W each.
Junction temp max: 125 degrees max
High fT? : 30MHz.
You blow up you amp, you can fix it if it's discrete. In the 1980s, 90s, 2000s and today in 2024. Big difference.
Long post, I know, but amplifiers, particularly power amplifiers, need devices and design that can withstand abuse and real world demands. That's why they are called "power" amplifiers.
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